Sleep occurs in 90-minute cycles. Waking at the end of a cycle feels refreshed; waking mid-cycle triggers hours of grogginess. This calculator finds the optimal alarm times for you.
Sleep stages, needs by age, and the science of getting quality rest.
| Age Group | Recommended Hours | Cycles | Notes |
|---|---|---|---|
| Children (3–13 years) | 9–11 hours | 6–7 cycles | Critical for growth and learning |
| Teenagers (14–17) | 8–10 hours | 5–6 cycles | Later natural circadian rhythm |
| Adults (18–64) | 7–9 hours | 5–6 cycles | Most common recommendation |
| Older Adults (65+) | 7–8 hours | 4–5 cycles | Earlier circadian rhythm shift |
| Stage | Type | Duration | What Happens | Why It Matters |
|---|---|---|---|---|
| Stage 1 | Light NREM | 1–7 min | Transition from wakefulness | Entry point to sleep |
| Stage 2 | Light NREM | 10–25 min | Heart rate slows; memory consolidation begins | Largest % of sleep |
| Stage 3 | Deep NREM (SWS) | 20–40 min | Growth hormone released; tissue repair | Physical restoration |
| Stage 4 | Deep NREM (SWS) | 20–40 min | Immune function boosted; memory consolidated | Immune & physical repair |
| Stage 5 | REM | 10–60 min | Dreaming; emotional processing; learning | Mental & emotional health |
Sleep occurs in cycles of approximately 90 minutes. This calculator adds your estimated sleep latency (time to fall asleep) to determine when complete cycles end, giving you the ideal alarm times. Both "sleep at a time" and "wake at a time" modes are supported.